LED lighting technology is rapidly developing to replace traditional incandescent and fluorescent lightings. LED tube lamps are mercury-free in comparison with fluorescent tube lamps that need to be filled with inert gas and mercury. Thus, it is not surprising that LED tube lamps are becoming a highly desirable illumination option among different available lighting systems used in homes and workplaces, which used to be dominated by traditional lighting options such as compact fluorescent light bulbs (CFLs) and fluorescent tube lamps. Benefits of LED tube lamps include improved durability and longevity and far less energy consumption; therefore, when taking into account all factors, they are typically considered a cost effective lighting option.
Typical LED tube lamps each have a variety of LED lamp components and driving circuits. The LED lamp components include LED chip-packaging elements, light diffusion elements, high efficient heat dissipating elements, light reflective boards and light diffusing boards. Heat generated by the LED lamp components and the driving elements is considerable and mainly dominates the illumination intensity such that the heat dissipation needs to be properly disposed to avoid rapid decrease of the luminance and the lifetime of the LED lamps. Problems including power loss, rapid light decay, and short lifetime due to poor heat dissipation tend to be key factors in consideration of improving the performance of the LED illuminating system. It is therefore one of the important issues to improve on the heat dissipation aspects of the LED products.
Nowadays, most LED tube lamps use plastic tubes and metallic elements to dissipate heat from the LEDs. The metallic elements are usually exposed to the outside of the plastic tubes. This design improves heat dissipation but heightens the risk of electric shocks. The metallic elements may be disposed inside the plastic tubes, however the heat still remains inside the plastic tubes and deforms the plastic tubes. Deformation of the plastic tubes also occurs even when the elements to dissipate heat from the LEDs are not metallic.
The metallic elements disposed to dissipate heat from the LEDs may be made of aluminum. However, aluminum is too soft to sufficiently support the plastic tubes when the deformation of plastic tubes occurs due to the heat as far as the metallic elements disposed inside the plastic tubes are concerned.
Current ways of using LED lamps such as LED tube lamps to replace traditional lighting devices (referring mainly to fluorescent lamps) include using a ballast-compatible LED tube lamp. Typically on the basis that there is no need to change the electrical or conductive wirings in the traditional lamps, an LED tube lamp can be used to directly replace e.g. a fluorescent lamp. Common main types of electronic ballast include instant-start ballast and program-start ballast. Electronic ballast typically includes a resonant circuit and is designed to match the loading characteristics of a fluorescent lamp in driving the fluorescent lamp. For example, for properly starting a fluorescent lamp, the electronic ballast provides driving methods respectively corresponding to the fluorescent lamp working as a capacitive device before emitting light, and working as a resistive device upon emitting light. But an LED is a nonlinear component with significantly different characteristics from a fluorescent lamp. Therefore, using an LED tube lamp with an electronic ballast impacts the resonant circuit design of the electronic ballast, causing a compatibility problem.
Further, circuit design of current LED tube lamps mostly doesn't provide suitable solutions for complying with relevant certification standards and for better compatibility with the driving structure using an electronic ballast originally for a fluorescent lamp. For example, since there are usually no electronic components in a fluorescent lamp, it's fairly easy for a fluorescent lamp to be certified under EMI (electromagnetic interference) standards and safety standards for lighting equipment as provided by Underwriters Laboratories (UL). However, there are a considerable number of electronic components in an LED tube lamp, and therefore consideration of the impacts caused by the layout (structure) of the electronic components is important, resulting in difficulties in complying with such standards.
Further, the driving of an LED uses a DC driving signal, but the driving signal for a fluorescent lamp is a low-frequency, low-voltage AC signal as provided by an AC powerline, a high-frequency, high-voltage AC signal provided by a ballast, or even a DC signal provided by a battery for emergency lighting applications. Since the voltages and frequency spectrums of these types of signals differ significantly, simply performing a rectification to produce the required DC driving signal in an LED tube lamp is not competent at achieving the LED tube lamp's compatibility with traditional driving systems of a fluorescent lamp.
In addition, for some LED tube lamps, rigid circuit board is typically electrically connected with their end caps by way of wire bonding, in which the wires may be easily damaged and even broken due to any move during manufacturing, transportation, and usage of the LED tube lamps and therefore may disable the LED tube lamps. Or, bendable circuit sheet may be used to electrically connect the LED assembly in the lamp tube and the power supply assembly in the end cap(s). The length of the lamp tube during manufacturing also needs to match for the bendable circuit sheet, and thus the variable factor increases in the manufacture of the lamp tube.
The heat generated by the LED tube lamp can be reduced through controlling the LED illumination and lighting period by an LED driving circuit. However, it is not easy to meet the expected LED illumination requirement based on some analog driving manners since the relationship between the LED illumination and the LED current is non-linear and color temperature of some LEDs changes according to LED current. Moreover, heat convection in the lamp tube is not easy performed, e.g., in some cases, the lamp tube is even a confined space, and once the LED illumination increases, the lifespan of the LED tube lamp shortens because the lifespan of LEDs is sensitive to temperature. Also, some LED driving circuits result in the circuit bandwidth getting smaller since the driving voltage/current repeatedly returns between the maximum and minimum. This may limit the minimum conducting period and affects the driving frequency.
In addition, the LED tube lamp may be provided with power via two ends of the lamp and a user can be easily electric shocked when one end of the lamp is already inserted into an terminal of a power supply while the other end is held by the user to reach the other terminal of the power supply.
As a result, currently applied techniques often fall short when attempting to address the above-mentioned worse heat conduction, poor heat dissipation, heat deformation, electric shock, weak electrical connection, smaller driving bandwidth, and variable factor in manufacture defects.